Drive system for crystal pickups



Fell 23, 1954 N. F. MARTIN DRIVE SYSTEM FOR CRYSTAL PICKUPS Filed Feb.17, 1949 Patented Feb. 23,vr 1954 2570,4012 DR'ILvE SYSTEM-'FORCRYSZUAL;PILCKUPS;

Norman'fF Martin;

corporation of Delaware This' invention` relatesv to phonograph pickupsandis-specically directed to the provision oa novel and? improvedcrystal pickup wherein the playing point-'ofthe pickup stylus andthevpiezoelectric'crystal driven'thereby are mechanically interconnected insuch a manner that'the stylus o'i'' motiontransmitti'ng means orresilientccnnection between'the playing'po'int and? thel crystal,` inorder that the yieldable nature of the motion transrniltting means wouldprovide sicent compliance' fr the playing pointi tb;- folloW the"vgrooveV of the record; with primary 0bjec`t`\ of? tli provide* thecrystal pickup pt'ed to utilize? a corn/entifo'nal crystallo'f' high ye; together with' alEl phbnfl having' a flexible 2'. vide@ apickup"Wl'ierehfthe-parts arefso designed', constructed and` related tb each?other that theenergy imparted to. the playing point of th'e st'yls isitrahsmitted t'o the crystal without .sube

tained;

It isl a Frther objectief the invention tel pro'- vide a crystal pickupwherein the effective mechanica-l iinped`s'ai1'-c'e'` Between' thecrystal and playing'point ofthe' stylixs is pr'cperlyf matched to'accomplishi niaxiinlim ener-'gyA transfer from a s'tylli-having adequatecompliance t'o acr'ys talof` relatively stiflfl andi rigidi nature'.

AnE additional object o'fft'he inventionl is" tov pro`-` vide" apiez'olelectrlccrystal'l pickup` having a styluslconsi'stingoif'alshort; slnder'wire having a;-1 ijesonafntl frequencyla'bov'e thelrange cf audibility; withl a driving c'o'nnectibn'-` consisting" off athin4` lnetallgstripi betveenl the' stylus and the Sltlsbthattl'elOpela'tiliglpart's of the device Hav/81 r-l'l'glgbl inerti@ aIld wll notresonate Withih the? range-of frequencies to bei reproduced;

'Fliese obects areiacco'nplished in the present invntr 5y? aVx noflCbialbn 0f parts' in which thelstylus GSiStis Cif Very short length c'sl'edi' Wire-'- (Which n'ee'dlno't be2 over 14" in overall length)mounted in a pivot bear-ing at itis` extremely? lowV inertia allows deiclfyf diie` to' th' atrfabl resonance of s'uclfia"y stylus is at afrequency." abdve audible' range and conseth'e rangeo frequencies' to bereproducetl sobrio objectionable characteristics of .seit-resonance areiencountered.

hsty-liii'sol th'epreSentTdiScloSure is alsodesignedto".functienasfanfimpedance matching deth'erf. playing point,which' should rela telly low'impeuanceto'the-record;

-cfyst itself.; which presents'a high im# friction or? inertia. Inaddition,-

electrical energy without substantial losses, yet to do this withmechanical instrumentalities capable of giving a fairly at frequencyresponse throughout the entire range of sounds to be reproduced.

Two somewhat different embodiments of the invention are illustrated inthe drawings of this disclosure wherein:

Figure 1 is a cross sectional view of the end of a phonograph tone armwith a pickup cartridge of the form preferred for use with a crys tal ofthe twister type; and A Figure 2 is a cross sectional view similar toFigure l showing the form of the invention presently preferred for usein connection with a crystal of the bender type.

In both embodiments of the invention the tone arm I is hollow,preferably being constructed of molded plastic. As shown, it is arrangedto provide a mounting for a crystal cartridge II consisting of a pair ofidentical and opposite housing portions I2 adjoined by the machinescrews or rivets I3, I4 and I5. The housing is provided with aninsulating block I5 in which output terminals I1 and I8 are mounted andthese terminals are electrically connected to the crystal by leads I9and 25J in a manner well understood in the art.

In the form of the invention shown in Figure lthe crystal 2| is mountedin a resilient mounting block 22 and is so oriented that its twistingaxis lies on its vertical center line. The lower edge of the crystal isclamped between a pair of opposite flanges 23 on a fitting generallydesignated as 24. The fitting 24 has a dual function. The righthandportion thereof acts as a mounting for the journal or pivot stud 25,while the lefthand portion functions as a crystal driving member. Thejournal 25 is supported by a bearing consisting of a resilient sleeve 26clamped in a suitable socket 21 in the cartridge housing so that thelower edge of the crystal is adequately supported yet may twist on itsaxis. That is, the crystal is restrained against lateral movement but iscapable of unrestricted twisting movement on the axis of the bearingsand journal 25.

The stylus 3l of the pickup consists of the short, slender piece of wirehaving an upwardly curved portion 32 terminating in a ball 33 held inthe resilient sleeve 34 which is also clamped in a socket 35 at a pointadjacent to the bearing 28 but spaced slightly to the left therefrom asviewed in the drawing. The end of the stylus opposite the stylus bearinghas a flattened portion 3l in which one or more stylus tips or playingpoints 38 and 39 are mounted.

In the precise form of the invention shown it is contemplated that thepoint 38 may have the tip shaped and dimensioned for use with records ofthe long playing or microgroove type while the tip 39 is suited to usewith standard records, so that the two points may be interchangeablyused by tilting the entire cartridge around the pivot eI so that eitherpoint may be placed in position to engage the record. It is to beunderstood, however, that the present specification is not directed tothis feature and that the invention here shown and claimed is applicableto the structure shown irrespective of whether one or more playingpoints are employed. It is :of importance, however, to note thattl'restylusac- -cording to these teachings may be a very small piece ofslender wire so-that its natural' resonant frequency will be above therange of audibility and consequently beyond the range of frequenciesthat the pickup is designed to reproduce, so that the quality ofreproduction will not be adversely affected by self-resonantcharacteristics of the stylus. At the same time this short length ofwire (which need not exceed 1A" between the ball 33 and playing point38) is sulciently stiff so that vibratory motion imparted to the playingpoint will not be lost by flexing of the stylus. Instead the energyimparted to the stylus tip will be transmitted upwardly through the thinsheet metal strip i2 from the stylus to the crystal driving member. Itfollows that substantially all of the energy imparted to the playingpoint will be effective to flex the crystal. It is to be noted that thestrip 42 engages the stylus at a point between the playing point 38 andthe stylus bearing. This provides suitable matching between therelatively high mechanical impedance of the crystal and the end of thestylus so that the playing point 33 may have adequate lateral complianceto accomplish faithful tracking in the record groove with a very lowtracking weight. Thus the stylus may track faithfully without needletalk and without causing undue record wear.

The form of the invention disclosed in Figure 2 differs from that justdescribed in that it employs a crystal 5l of the bender type mounted ina resilient mounting block 52 at the side adjacent the output terminals.The stylus 53 may be of the same general form as the stylus 3I and asshown is provided with a bearing comprising a ball 54 mounted in aresilient sleeve 55 clamped in the cartridge housing. The opposite endof the stylus is flattened at 5G and carries playing points 51 and 58.

The driving connection from the stylus to the crystal is completedthrough the thin metal strip 59 extending upwardly from the midpoint onthe stylus and secured to a crystal driving member having oppositeflanges 50 clamped to the lower corner of the crystal 5I. The mode ofoperation of this form of the invention is identical with that of theform shown in Figure 1 with the exception that the energy transmitted tothe crystal driving member 5B serves to bend the crystal rather than totwist it.

From the foregoing it will be seen that the teachings of the presentinvention provide a convenient and simplified means for reconciling theheretofore conilicting characteristics of mechanical impedanceencountered in typical crystal pickups, and provide means tosuccessfully match the mechanical impedances of the mechanism so thatall of the energy imparted to a playing point having the required degreeof compliance may be effectively transmitted to a crystal which isinherently stiif in nature and adapted to only very limited flexingmovements. Moreover, this object of the invention is accomplished by theprovision of a mechanism of simple mechanical design with the individualparts so arranged and constructed that the unit has no point ofselfresonance within the range of sounds to be reproduced. This not onlyincreases the efciency of the unit and overcomes the diicultiescustomarily associated with mechanisms having parts of considerableinertia but also prevents the eccentricities of performance normallyencountered in any device having a period of mechanical. resonance at afrequency within .the reproduction range.

The characteristics of frequency response may compliance, output and bevaried as required by altering the dimensional relationships of thestylus and driving connection to the crystal and may also be controlledby the use of a stylus pivot bearing which has, in itself, some degreeof lateral compliance and resistance, that is, the bearings 34 and 55may be true pivots if desired, but in certain instances it is advisableto utilize bearing material having considerable inherent resiliency sothat these do not function as a true pivot but allow a certain degree oflateral compliance at the pivoted end of the stylus.

It is also to be remembered that while the teachings of this inventioniind their greatest utility in connection with type, yet these teachingsare equally applicable to other electro-mechanical transducers and maybe used to advantage in any application where the normal mechanicalimpedance of the transducer unit is higher than the desired mechanicalimpedance of the stylus tip. It is therefore pointed out that while theinvention has been described and illustrated in the present preferredembodiment it is not limited to the precise structure shown anddescribed but extends to any variation or modication thereof within theterms of the appended claims.

Having thus described the invention, I claim:

1. In a phonograph pickup, in combination, a cartridge comprising ahousing, a crystal mounting within the housing; a crystal bearing in thehousing remote from said mounting; and a stylus bearing remote from thecrystal mounting and adjacent the crystal bearing; a piezo-electriccrystal xed in said crystal mounting and supported by said bearing, witha crystal driving member secured to said crystal at a point remote fromsaid mounting; a stylus consisting of a short slend-er wire having aresonant frequency above the range of audibility, said wire having oneof its ends pivoted in the stylus bearing and having a playing pointnear the other end; and a driving connection consisting of a thin metalstrip extending between the stylus and the crystal driving member andengaging the stylus between the playing point and the stylus bearing.

2. In a phonograph pickup, in combination, a cartridge comprising ahousing, a crystal mounting within the housing; a crystal bearing in thehousing remote from said mounting; and a stylus bearing remote from thecrystal mounting and adjacent the crystal bearing; a piezoelectriccrystal xed in said crystal mounting and supported by said bearing, witha crystal driving member secured to said crystal at a point remote fromsaid mounting; a stylus consisting of a short slender wire having aresonant frequency above the range of audibility, said wire beingpivoted in the stylus bearing and having a playing point near one endthereof; with a driving connection consisting of thin metal stripbetween the stylus and the crystal driving member; said connection beingspaced from the stylus bearing less than the spacing between the stylusbearing and the playing point.

3. In a phonograph pickup, in combination, a cartridge comprising ahousing, a crystal mounting within the housing; and a stylus bearingremote from said crystal mounting; a piezoelectric crystal xed in saidcrystal mounting pickups of the crystal d with a crystal driving membersecured to said crystal at a point remote from said mounting; a stylusconsisting of a short slender wire pivoted in the stylus bearing andhaving aA playing point nearone end thereof; and a driving connectionbetween the stylus and the crystal driving mernber at a point betweenthe ends of the stylus; said connection being spaced from the stylusbearing less than the spacing between the stylus bearing and the playingpoint.

4. In a phonograph pickup, in combination, a cartridge comprising ahousing, a crystal mounting within the housing; and a stylus bearingremote from said crystal mounting; a piezoelectric crystal xed in saidcrystal mounting with a crystal driving member secured to said crystalat a point remote from said mounting; a stylus consisting of a shortslender wire pivoted in the stylus bearing and having a playing pointnear one end thereof; and a driving connection between the stylus andthe crystal driving member at a point between the ends of the stylus.

5. In a phonograph pickup, in combination, a cartridge comprising ahousing, a crystal mounting within the housing; a crystal bearing in thehousing remote from said mounting; and a stylus bearing remote from thecrystal mounting and adjacent the crystal bearing; a piezo-electriccrystal xed in said crystal mounting and supported by said bearing, witha crystal driving member secured to said crystal at a point remote fromsaid mounting; a stylus having a resonant frequency above the range ofaudibility pivoted in the stylus bearing and having a playing point nearone end thereof; and a driving connection between the stylus and thecrystal driving member; said connection being spaced from the stylusbearing less than the spacing between the stylus bearing and the playingpoint.

`6. In a phonograph pickup, in combination, a cartridge comprising ahousing, a crystal mounting within the housing; a crystal bearing in thehousing remote from said mounting; and a stylus bearing remote from thecrystal mounting and adjacent the crystal bearing; crystal xed in saidcrystal ported by said bearing, with a crystal driving member secured tosaid crystal at a point remote from said mounting; a stylus pivoted inthe stylus bearing and having a playing point near one end thereof; anda driving connection between the stylus and the crystal driving member;said connection being spaced from the stylus bearing less than thespacing between the stylus bearing and the playing point.

NORMAN F. MARTIN.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date Re. 20,680 Sawyer Mar. 29, 1938 2,105,011 Williams Jan. l1,1938 2,181,437 Norton Nov. 28, 1939 2,207,539 Gravley July 9, 19402,415,403 Backman Feb. 11, 1947 2,471,601 Albright May 31, 19492,518,861 Burtch Aug. 15, 1950 2,564,054 Dreisbach Aug. 14, 19512,575,999 Cordes Nov. 20, 1951

